A curved spring warmth response of US lilac leaf-to-bloom gaps was uncertain in four samples from 1965 to 2008

We tested whether the response of the time from first leaf to first bloom changed with spring warmth. Four US lilac region and period samples used 5,715 paired plant-years from 1965 to 2008. Models had plant and year effects, winter temperature, and linear and squared spring temperature terms. The four squared-term estimates ranged from -0.250 to -0.124 days per C squared. All four intervals included zero after correction for four tests. March-April checks gave negative intervals in both early samples, but these results did not repeat in the later samples. The data do not establish a common curved response. Unknown visits, selected long records, different lilac types by region, coarse monthly weather, and approximate cluster intervals limit inference. This is a seasonal weather test. It does not measure daily extremes, pollution, community diversity, or a causal climate-change effect. The package contains a paired panel, source hashes, code, all results, a figure, and independent coefficient checks.

phenology · lilac · temperature · curvature · observation bias · null result